1. Field of the Invention
The present invention relates to a damper mechanism. More specifically, the present invention relates to a damper mechanism for absorbing and damping torsional vibrations while also transmitting torque.
2. Background Information
Conventional clutch disk assemblies used in vehicles have two basic functions. One function is to serve as a clutch for engaging with and disengaging from the flywheel. The other basic function is to serve as a damper mechanism for absorbing and damping torsional vibrations from the flywheel. In general, vehicle vibrations include idling-related noises (rattling sounds), traveling-related noises (rattling associated with acceleration and deceleration and muffled noises), and tip-in/tip-out (low frequency vibrations). The function of the clutch disk assembly as a damper is to eliminate these noises and vibrations.
Idling-related noises are rattling noises that emit from the transmission when the gear shift is put into neutral and the clutch pedal is released, for example while waiting at a traffic light. When the engine is running at a speed in the vicinity of idling speed, the engine torque is low and the torque change at the time of each explosion in the pistons of the engine is large. Thus, idling-related noises are generated. Under these conditions, the teeth of the transmission input gear and counter gear undergo a phenomenon of striking against one another.
Tip-in and tip-out (low frequency vibrations) refer to large-scale lengthwise shaking of the vehicle that occurs when the accelerator pedal is depressed or released suddenly. If the rigidity of the drive transmission system is low, the torque transmitted to the tires is transmitted back from the tires as torque and the resulting lurching reaction causes excessive torque to be generated at the tires. As a result, longitudinal vibrations that shake the vehicle on a large scale back and forth occur in a transitional manner.
In the case of idling noises the problem lies in the vicinity of the zero torque portion of the torsion characteristic of the clutch disk assembly. It is usually better for the torsional rigidity to be low. Conversely, it is necessary for the torsion characteristic of the clutch disk assembly to be as rigid as possible to suppress the longitudinal vibrations caused by tip-in and tip-out.
In order to solve this problem, a clutch disk assembly has been proposed which has a two-stage characteristic obtained by using two types of spring members. The first stage or low twisting angle region of the torsion characteristic has a low torsional rigidity and low hysteresis torque and thus provides a noise preventing effect during idling. Meanwhile, the second stage or high twisting angle region of the torsion characteristic has a high torsional rigidity and high hysteresis torque and is thus sufficiently capable of damping the longitudinal vibrations of tip-in and tip-out.
Also known is a damper mechanism that efficiently absorbs small torsional vibrations during the second stage of the torsion characteristic by not allowing the large friction mechanism of the second stage to operate when small torsional vibrations are inputted due to such factors as combustion fluctuations in the engine.
In order to prevent the large friction mechanism from operating when small vibrations are transmitted due to, for example, engine combustion fluctuations, it is necessary for the high-rigidity spring member to be compressed and for a rotational gap of a prescribed angle to be secured between the high-rigidity spring member and the large friction mechanism.
The angular magnitude of this rotational gap is relatively small, i.e., approximately 0.2 to 1.0 degrees. The rotational gap exists in both the positive side second stage, which corresponds to the input plate being twisted in the rotational drive direction (positive direction) with respect to the spline hub, and the negative side second stage, which corresponds to the input plate being twisted in the opposite direction (negative direction) with respect to the spline hub.
Conventionally, the rotational gap is realized using the same mechanism on both the positive side second stage and the negative side second stage. Consequently, the rotational gap is always produced on both the positive side and the negative side of the torsion characteristic. However, depending on the characteristics of the vehicle, there are situations where it is preferred that the magnitude of the rotational gap be different on the positive and negative sides of the torsion characteristic. It is also possible to have a situation where it is desirable not to provide the rotational gap at all on one side, i.e., either the positive side or the negative side. More specifically, the situation would call for having the rotational gap on the negative side of the torsion characteristic in order to reduce the peak vibrations that occur at the resonance rotational speed during deceleration. However, in front-engine and front-drive or FF vehicles, the resonance peak often remains in the region of practical engine speeds and the noise and vibration performance in the vicinity of the resonance rotational speed will worsen if a rotational gap is provided on the positive side of the torsion characteristic. Meanwhile, the tip-in and tip-out damping performance will degrade if the damper mechanism is structured such that high hysteresis is not produced on the negative side of the torsion characteristic.
In view of the above, there exists a need for a damper mechanism that overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.